The present invention relates to a continuous flow analyzing method and apparatus, and more particularly to an analyzing method and apparatus for performing an automatic measurement with high precision over a wide quantitative measurement range. More particularly, the invention relates to a continuous analyzing method and apparatus using a flow injection method.
According to a flow injection analyzing method, a continuous flow of controlled carrier is prepared by using a constant flow rate pump, a sample is injected into the flow and reacted with a color reagent or the like, if necessary, and the continuous flow containing the sample is introduced into a detector to thereby carry out quantitative measurement of the target components. Since the reaction with the reagent, the introduction into the detector, the discharge and the like are automatically carried out after the injection of the reagent, the flow injection analyzing method has the advantage that a large amount of samples can be automatically and quickly measured and is used in a wide range of applications including analyses from clinical research and use in determining public pollution.
However, in the above-described method, the quantitative measurement itself is carried out by a detector interposed in the flow path and the detection precision depends, therefore, upon the detection method (in general, absorptiometry, fluorophotometry, atomic absorption spectrometry, flame photometry, ICP emission spectrophotometrical analysis, ICP mass spectrometric analysis) and the characteristics of the detector used in the method. Accordingly, it is necessary to control the sample solution and the arrangement and structure of the analyzing system such that quantitative analysis by the detector is most precisely carried out.
More specifically, in the case where it is expected in advance that the target component in the sample has a high or low concentration, it is necessary to dilute or condense the sample solution in a batch manner or to change the reaction path (reaction coil length or the like) or to control the detection sensitivity of the detector or the injection amount of the sample. Among these approaches, with the batch manner concentration adjustment or the change or adjustment of the arrangement of the apparatus, a long time and a large amount of work are required. Thus, the advantage of the automatic system can not be enjoyed. Accordingly, it is desirable to provide a practical method for controlling the sample injection amount and the measurement concentration.
In a measurement system of a general flow injection method, a measurement container (sample loop) filled with sample for a predetermined capacity is juxtaposed with the carrier flow path for switching the carrier flow to the sample loop side, and the entire amount of the sample filled in the sample loop is extruded for introduction with the carrier flow into a measurement system. It is therefore possible to change the sample injection amount by changing the capacity of the sample loop. The change of the capacity of the sample loop can be carried out by changing the length of tubes used therein for each sample. More specifically, the tubes are exchanged for every sample, or otherwise a syringe-like variable capacity portion is provided in a part of the sample loop (see Japanese Patent Application Laid-Open No. Sho 59-3359 or Japanese Examined Patent Publication No. Hei 2-15031). However, the former method is troublesome and is not suitable for the purpose of processing a large amount of sample in a short period of time. Also, the latter method suffers from a disadvantage that a sample having a high salt concentration tends to clog the path since the structure of the sample injection portion is complicated. Also, it is difficult to automatically control the injection amount.
A method is also known in which the injection amount is adjusted by injecting the sample from the outside of the flow path into the carrier flow path for a predetermined period of time. J. L. Burugera et al. (Anal. Chem. Acta., 234, 253, 1990) and M. L. Guardia et al. (Fresenius' Z. Anal, Chem., 345, 579, 1993) disclose an apparatus using a variable volume injector in which sample measurement holes having different volumes are provided in a rotor for that purpose. Also, Japanese Patent Application Laid-Open No. Hei 5-302871 discloses an apparatus provided with a flow path switching valve. However, in the former apparatus, the sample can be injected only by a predetermined standard volume. In any case, it is difficult to exactly inject the amount of the sample needed for the measurement.
It has also been proposed to use a method in which a sample is first injected into a diluent flow, and only the portion corresponding to a predetermined range of the concentration gradient is introduced into the carrier flow by utilizing the concentration gradient of the sample formed in the diluent flow (Japanese Patent Application Laid-Open No. Hei 4-77662). However, the dispersion of the sample in the diluent flow is not always simple. According to such a method, it is difficult to determine which part of the diluent flow is picked up. In order to calculate the concentration of the original sample from the obtained measurement values, it is necessary to consider a number of factors such as viscosity of the sample, flow resistance of the flow system and the like. A large measurement error is inevitable.
Also, in any method, since the sample injection amount is set in advance corresponding to a range of the concentration which is usually expected from the origin of the sample, even in the case where a large amount of the sample is quickly processed, it is necessary to set the sample loop length or the variable capacity in conformity with each sample, which is troublesome. Furthermore, since there is an inevitable physical limit in setting the sample loop length or the variable capacity, the switching of the sample injection amount has to be carried out in a batch manner. It is impossible to effect continuous measurement. In view of this fact, if the injection amount can be changed as desired without exchanging sample loops, it will be quite convenient.